Block parameters in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of block parameters with multiple variables

What is the output of this Ruby code?

Ruby

def test
  yield(1, 2)
end

result = []
test do |a, b|
  result << a + b
end

puts result.first

A 2

B 1

C nil

D 3

💡 Hint

Remember that block parameters receive values passed by yield in order.

The method yields two values, 1 and 2, which are assigned to a and b respectively. Adding them gives 3.

❓ Predict Output

intermediate

Block parameters with array destructuring

What will this Ruby code print?

Ruby

def example
  yield([10, 20])
end

example do |(x, y)|
  puts x * y
end

A 10

B 1020

C 200

D Error

💡 Hint

The block parameter uses parentheses to destructure the array.

The array [10, 20] is destructured into x=10 and y=20, so x * y is 200.

❓ Predict Output

advanced

Block parameters with default values

What is the output of this Ruby code?

Ruby

def call_block
  yield(5)
end

call_block do |a, b = 10|
  puts a + b
end

A 15

B Error

C 5

D 10

💡 Hint

Check how default values work in block parameters when fewer arguments are passed.

Only one argument (5) is passed, so a=5 and b uses default 10. Sum is 15.

❓ Predict Output

advanced

Block parameters with splat operator

What will this Ruby code output?

Ruby

def run_block
  yield(1, 2, 3)
end

run_block do |a, *rest|
  puts rest.sum + a
end

A Error

B 6

C 3

D 5

💡 Hint

The splat operator collects remaining arguments into an array.

a=1, rest=[2,3], sum of rest is 5, plus a is 6.

❓ Predict Output

expert

Block parameters with nested destructuring and default values

What is the output of this Ruby code?

Ruby

def complex
  yield([1, 2], 3)
end

complex do |(a, b = 5), c|
  puts a + b + c
end

A 6

B 7

C Error

D 8

💡 Hint

Look carefully at how default values apply inside nested destructuring.

The first argument is [1,2], so a=1, b=2 (default 5 ignored because array provides value), c=3. Sum is 1+2+3=6.

Practice

1.

What are block parameters in Ruby?

Choose the best description.

easy

A. Variables inside | | that receive values passed to the block.

B. Methods that define how a block works.

C. Special keywords to start a block.

D. Constants used only outside blocks.

Solution

1. Step 1: Understand block parameters role

   Block parameters are variables placed inside | | after do or { to receive values passed into the block.

2. Step 2: Compare options with definition

   Only Variables inside | | that receive values passed to the block. correctly describes block parameters as variables inside | | that get values passed to the block.

3. Final Answer:

   Variables inside | | that receive values passed to the block. -> Option A

4. Quick Check:

   Block parameters = variables inside | | [OK]

Hint: Block parameters are always inside | | after do or { [OK]

Common Mistakes:

• Confusing block parameters with methods
• Thinking block parameters are keywords
• Assuming block parameters are constants

2.

Which of the following is the correct syntax for block parameters in Ruby?

array.each do ?

easy

A. [item] puts item

B. (item) puts item

C. |item| puts item

D. {item} puts item

Solution

1. Step 1: Recall block parameter syntax

   Block parameters are placed inside vertical bars | | after do or {.

2. Step 2: Match syntax with options

   Only |item| puts item uses |item| which is the correct syntax for block parameters.

3. Final Answer:

   |item| puts item -> Option C

4. Quick Check:

   Block parameters use | | [OK]

Hint: Block parameters always go inside | | after do or { [OK]

Common Mistakes:

• Using parentheses () instead of | |
• Using curly braces {} for parameters
• Using square brackets [] for parameters

3.

What is the output of this Ruby code?

numbers = [1, 2, 3]
numbers.each do |n|
  puts n * 2
end

medium

A. 2
4
6

B. 1
2
3

C. Error: undefined variable n

D. nil

Solution

1. Step 1: Understand the block parameter usage

   The block parameter n takes each element from the array numbers one by one.

2. Step 2: Calculate output for each element

   For each n, the code prints n * 2. So outputs are 2, 4, and 6 on separate lines.

3. Final Answer:

   2 4 6 -> Option A

4. Quick Check:

   Each number doubled = 2,4,6 [OK]

Hint: Block parameter holds each item; multiply inside block [OK]

Common Mistakes:

• Confusing block parameter with array variable
• Expecting original numbers printed
• Thinking block parameter is undefined

4.

Find the error in this Ruby code:

fruits = ['apple', 'banana']
fruits.each do fruit|
  puts fruit
end

medium

A. Block parameter should be in parentheses

B. Missing closing | after block parameter

C. No error, code runs fine

D. Missing opening | before block parameter

Solution

1. Step 1: Check block parameter syntax

   Block parameters must be enclosed inside vertical bars | |. Here, only the closing bar is present.

2. Step 2: Identify missing part

   The opening | before fruit is missing, causing a syntax error.

3. Final Answer:

   Missing opening | before block parameter -> Option D

4. Quick Check:

   Block parameters need both | | [OK]

Hint: Block parameters always need both | at start and end [OK]

Common Mistakes:

• Forgetting the opening |
• Using parentheses instead of | |
• Assuming code runs without |

5.

Given this code, what will be the output?

pairs = [[1, 2], [3, 4], [5, 6]]
pairs.each do |a, b|
  puts a + b
end

hard

A. [1, 2]
[3, 4]
[5, 6]

B. 3
7
11

C. Error: wrong number of block parameters

D. 1
3
5

Solution

1. Step 1: Understand multiple block parameters

   The block parameters a and b receive each inner array's two elements separately.

2. Step 2: Calculate sum for each pair

   For each pair, the code prints the sum: 1+2=3, 3+4=7, 5+6=11.

3. Final Answer:

   3 7 11 -> Option B

4. Quick Check:

   Sum of pairs = 3,7,11 [OK]

Hint: Use multiple block parameters to unpack arrays inside each [OK]

Common Mistakes:

• Expecting array printed instead of sum
• Thinking block parameters can't unpack arrays
• Assuming syntax error with two parameters